Method and apparatus for selecting link adaptation parameters for cdma-based wireless communication systems

ABSTRACT

A method and apparatus enhance the selection of transport block set size (TBSS), number of spreading codes, and modulation type, referred to collectively as transport format resource combination (TFRC), in a medium access control (MAC) layer for transmission of data in a code division multiple access (CDMA) wireless communication system, preferably a Universal Mobile Telecommunications Systems (UMTS) high speed downlink packet access (HSDPA) communication system. The maximum number of spreading codes available for transmission and the set of possible TFRCs are preferably determined based on a channel characteristics provided in part by a channel quality indicator (CQI). For each TBSS value in the set of possible TFRCs, a TFRC is selected with the largest number of spreading codes within the maximum number of spreading codes for which the corresponding coding rate is preferably at least ⅓. The corresponding code rate for each selected TFRCs is compared to a threshold to select a corresponding type of modulation. One of the selected TFRCs is selected to be provided to the PHY layer that best matches the CQI and preferably has a maximum TBSS.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional PatentApplication No. 60/795,300 filed on Apr. 27, 2006 which is incorporatedby reference as if fully set forth.

FIELD OF INVENTION

The present invention is related to medium access control in wirelesscommunication systems. More particularly, the present invention is amethod and apparatus for selecting link adaptation parameters in amedium access control (MAC) layer in code division multiple access(CDMA) wireless communication systems.

BACKGROUND

Wireless communication systems are well known in the art. Communicationsstandards are developed in order to provide global connectivity forwireless systems and to achieve performance goals in terms of, forexample, throughput, latency and coverage. One current standard inwidespread use, called Universal Mobile Telecommunications Systems(UMTS), was developed as part of Third Generation (3G) Radio Systems,and is maintained by the Third Generation Partnership Project (3GPP).

A typical UMTS system architecture in accordance with current 3GPPspecifications is depicted in FIG. 1. The UMTS network architectureincludes a Core Network (CN) interconnected with a UMTS TerrestrialRadio Access Network (UTRAN) via an Iu interface. The UTRAN isconfigured to provide wireless telecommunication services to usersthrough wireless transmit receive units (WTRUs), referred to as userequipments (UEs) in the 3GPP standard, via a Uu radio interface. TheUTRAN may have one or more radio network controllers (RNCs) and basestations, referred to as Node Bs by 3GPP, which collectively provide forthe geographic coverage for wireless communications with UEs. One ormore Node Bs may be connected to each RNC via an Iub interface. RNCswithin a UTRAN communicate via an Iur interface.

One type of air interface defined in the UMTS standard is wideband codedivision multiple access (W-CDMA). In a W-CDMA system baseband signalsare spread in the frequency domain using orthogonal spreading codesprior to transmission, and despread at a receiver using the samespreading codes.

The Uu radio interface of a 3GPP system uses transport channels (TrCHs)for transfer of user data and signaling between UEs and Node Bs. Uplinkrefers to signaling from a UE to a Node B, and downlink transmissionsare from a Node B to a UE. In 3GPP communications, TrCH data is conveyedby one or more physical channels defined by mutually exclusive physicalresources, or shared physical resources in the case of shared channels.In a conventional 3GPP system, communications between a UE and a Node Bare conducted using a single data stream defined by a combination ofTrCHs called a coded composite TrCH (CCTrCH). Typically, a Node B isconcurrently communicating with several UEs using respective CCTrCH datastreams.

TrCH data is transferred in sequential groups of transport blocks (TBs)defined as transport block sets (TBSs). Each TBS is transmitted in agiven transmission time interval (TTI) which may span a plurality ofconsecutive system time frames. The number of bits in a TBS is calledthe transport block set size (TBSS).

UMTS specification releases 5 and 6 pertain to high speed downlinkpacket access (HSDPA) and high speed uplink packet access (HSUPA),respectively. HSDPA is a downlink packet access protocol for packetbased UMTS wireless communication systems employing a W-CDMA airinterface with a spreading factor (SF) of 16. According to HSDPA, up to15 spreading codes may be allocated to data for transmission in a commonTTI. The data may be modulated using either quadrature phase shiftkeying (QPSK) modulation or 16 quadrature amplitude modulation (16-QAM).In future releases of the HSDPA standard, it is expected that additionaltypes of higher order modulation will also be supported, such as 64quadrature amplitude modulation (64-QAM). Fast retransmissions areaccomplished according to hybrid automatic repeat request (HARQ) byretransmission combining, which enables operation at relatively highBlock Error Rates (BLER).

FIG. 2 is a block diagram of a communication system 100 in which a basestation 110 is communicating with a WTRU 120 over a Uu air interfaceaccording to the current HSDPA standard. For illustrative purposes,protocol layers are shown in the base station 110 including physicallayer (PHY) components 102, medium access control (MAC) layer components104, and higher layer components 106 which include a radio link control(RLC) layer. Adjacent layers in the protocol stack communicate with eachother. The MAC layer components 104 are responsible for mapping datastreams 105 (also called logical channels) from the higher layercomponents 106 to transport channels 107 provided to the PHY layer 102for physical transmission over the wireless channel.

The MAC layer also selects the transport format (TF) and link adaptationparameters for data transmission including transport block set size(TBSS), number of spreading codes, and modulation type that arecollectively referred to as transport format resource combination(TFRC). As described in accordance with the present invention below,selection of TFRC is preferably performed in the MAC layer by a TFRCselection function component 108 prior to each TTI. The selected TFRCparameters 109 are provided to the PHY layer 102 so that they may beused in the physical transmission of data 114 to the WTRU 120 in acommon TTI by way of TBs.

TFRC selection is based at least in part on characteristics of thephysical channel and is not fixed for a given data packet size.Information regarding the physical channel is provided by WTRU 120. WTRU120 takes channel quality measurements, such as determining the maximumexpected data rate, of the downlink channel and transmits acorresponding channel quality indicator (CQI) 122 to the base station110.

The CQI is typically represented as an integer value from 1 to 30, whereeach CQI value has a predetermined mapping to a TFRC including a TBSS, acorresponding number of spreading codes and a corresponding type ofmodulation that is known at WTRU 120 and base station 110. This mappingalso depends on the physical capabilities of WTRU 120, and a WTRU istypically assigned to a physical layer category based on its receivercapabilities such as the maximum supported number of received bits perTTI and the maximum supported number of spreading codes per TTI. 3GPPTechnical Standard (TS) 125.214 provides CQI mapping tables fordifferent WTRU physical layer categories (referred to as UE categories)and UE categories are described in 3GPP TS 125.306. For illustrationpurposes, an example CQI mapping for UE category 10 is given in Table 1.

The WTRU selects the CQI value for which the TFRC mapping is determinedto most closely match the maximum expected data rate on the downlinkchannel while satisfying a minimum desired TB success probability, whichrefers to the desired success rate of decoding received TBs at WTRU 120.The same TB success probability is typically known at WTRU 120 and basestation 110, and is preferably equal to 0.9 according to existing HSDPAstandards. To compare a TFRC to the maximum expected data rate of thedownlink channel, a corresponding expected data rate for the TFRCs inthe mapping table can be determined in advance, for example viasimulation.

The CQI value 122 reported by WTRU 120 to base station 110 is providedto the MAC layer 104 via the PHY layer 102, and the TFRC selectionfunction 108 selects a TFRC 109 that best achieves the maximum expecteddata rate of the channel as determined by the CQI value and its mapping.While the CQI mapping table, as in Table 1 for example, indicates apreferred TFRC for a given CQI according to conventional TFRC selectionapproaches for HSDPA, the TFRC parameters of TBSS, number of spreadingcodes, and modulation are mutually dependent. Therefore, multipledifferent TFRCs may be able to match the desired channel characteristicscorresponding to a given CQI level, including maximum expected data rateand TB success probability.

TABLE 1 CQI mapping table for UE category 10 according to 3GPP TS125.214. Number of spreading CQI TBSS codes Modulation 0 N/A Out ofrange 1 137 1 QPSK 2 173 1 QPSK 3 233 1 QPSK 4 317 1 QPSK 5 377 1 QPSK 6461 1 QPSK 7 650 1 QPSK 8 792 2 QPSK 9 931 2 QPSK 10 1262 2 QPSK 11 14833 QPSK 12 1742 3 QPSK 13 2279 3 QPSK 14 2583 4 QPSK 15 3319 4 QPSK 163565 5 16-QAM 17 4189 5 16-QAM 18 4664 5 16-QAM 19 5287 5 16-QAM 20 58875 16-QAM 21 6554 5 16-QAM 22 7168 5 16-QAM 23 9719 7 16-QAM 24 11418 816-QAM 25 14411 10 16-QAM 26 17237 12 16-QAM 27 21754 15 16-QAM 28 2337015 16-QAM 29 24222 15 16-QAM 30 25558 15 16-QAM

Conventional strategies for selecting a TFRC 109 include choosing afewer number of spreading codes N than the maximum number of availablespreading codes M because the total allocated power Pt is divided amongthe N used spreading codes. Therefore it is believed that receivedsignal quality is better when more power is allocated per spreadingcode.

The inventor has recognized, however, that higher power for eachspreading code increases interference with the other spreading codes inthe channel, and employing fewer spreading codes does not necessarilyprovide better performance results, particularly in receivers employingadvanced decoding techniques. Existing TFRC selection procedures do nottake into account the interference effects of simultaneous transmissionsusing different spreading codes or the capabilities of advancedreceivers. Therefore, a procedure for TFRC selection that improves uponthe existing techniques is desired.

SUMMARY

The present invention provides a method and apparatus for transportformat resource combination (TFRC) selection in a medium access control(MAC) layer that enhances channel capacity. TFRC selection includesselection of transport block set size (TBSS), number of spreading codes,and modulation type for data transmission. The maximum number ofspreading codes available for transmission and the set of possible TFRCsare determined based on channel characteristics of the downlink channelprovided by the physical (PHY) layer. For each TBSS value in the set ofpossible TFRCs, a TFRC is selected with the largest number of spreadingcodes within the maximum number of spreading codes for which thecorresponding coding rate is preferably at least ⅓. The correspondingcode rates for the selected TFRCs are compared to thresholds to select atype of modulation. Finally, one of the selected TFRCs is selected to beprovided to the PHY layer that best matches downlink channel quality andpreferably with the largest TBSS in order to maximize the throughput.The present invention is preferably used in Universal MobileTelecommunications Systems (UMTS) high speed downlink packet access(HSDPA) communication systems, or in a wireless communication systememploying code division multiple access (CDMA).

Other objects and advantages will be apparent to those of ordinary skillin the art based upon the following description of presently preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an overview of the system architecture of a conventionalUniversal Mobile Telecommunications Systems (UMTS) network.

FIG. 2 is a block diagram of an example communication system 100 inwhich a base station 110 is communicating with a WTRU 120 in accordancewith the present invention.

FIG. 3 illustrates a graph of measured channel throughput versussignal-to-noise ratio (SNR) at a receiver for various modulationtechniques, which may be used to select a preferred type of modulationfor a transport format resource combination (TFRC) in accordance withthe present invention.

FIG. 4A is a flow diagram of a method for generating and selecting TFRCsin accordance with the present invention.

FIG. 4B is a flow diagram of a method for selecting a type of modulationfrom among quadrature phase shift keying (QPSK), 16 quadrature amplitudemodulation (16-QAM) and 64 quadrature amplitude modulation (64-QAM) tobe associated with a TFRC in accordance with the present invention.

FIG. 5 shows the measured throughput on a downlink CDMA channel usingthe existing 3GPP CQI mapping as given in Table 1 compared to themeasured throughput for the optimized CQI mapping generated according tothe present invention in Table 2 for a category 10 UE for a range ofaverage SNR values and for a TB success probability of 0.9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As used herein, a wireless transmit/receive unit (WTRU) includes but isnot limited to a user equipment, mobile station, fixed or mobilesubscriber unit, pager, cellular telephone, personal digital assistant(PDA), computer, or any other type of device capable of operating in awireless environment. A base station is a type of WTRU generallydesigned to provide network services to multiple WTRUs and includes, butis not limited to, a Node B, site controller, access point or any othertype of interfacing device in a wireless environment.

The present invention provides an information theoretic approach toselecting a more optimal transport format resource combination (TFRC) ina wireless communication system, where TFRC includes transport block setsize (TBSS), number of spreading codes, and modulation type for datatransmission over a wireless code division multiple access (CDMA)channel on a common transmission time interval (TTI) boundary. Althoughthe present invention is described herein with reference to high speeddownlink packet access (HSDPA) for downlink communications in UMTSsystems, the disclosed TFRC selection procedure has broaderapplicability and is applicable to general CDMA wireless communicationsystems including Third Generation Partnership Project (3GPP) CDMA2000and high speed packet access evolution (HSPA+) systems. The presentinvention may be used in both uplink (UL) and downlink (DL)communications, and therefore may be readily be implemented in WTRUsconfigured as user equipments (UEs) or base stations, such as Node Bs.

Preferably, an optimum number of spreading codes N is selected for TFRCaccording to the number of spreading codes that maximize the informationtheoretic channel capacity. To derive this capacity, the communicationchannel can be assumed to be an additive white Gaussian noise (AWGN)channel with bandwidth B such that the power Pt of the transmitter isfixed. Data is transmitted over bandwidth B using N different orthogonalspreading codes such that N is less than or equal to the maximum numberof available spreading codes M. In HSDPA, the maximum number ofavailable spreading codes M is at most 15.

A signal transmitted over the communication channel using N orthogonalspreading codes can be modeled by N separate corresponding propagationchannels, each with bandwidth B/M. Because the spreading codes areorthogonal, the noise on each of the propagation channels after thedespreading of the signal is uncorrelated and has equal power. If Arepresents the total signal-to-noise ratio (SNR) of the communicationchannel, the SNR of each individual propagation channel is proportionalto A/N because the total allocated power Pt is shared equally over the Nspreading codes. Adaptive modulation and coding (AMC) can be appliedindividually to each propagation channel along with advanced receiverand coding techniques to achieve a channel capacity close to thetheoretical upper limit of B/M*log(1+A/N) (known as Shannon's capacityformula). It then follows that the capacities of each of the propagationchannels C₁, . . . , C_(N) are the same and proportional to(1/M)*log(1+A/N). According to this result, propagation channelcapacities C₁, . . . , C_(N) slowly decrease as N increases. The totalcapacity C, however, is proportional to N*(1/M)*log(1+A/N), which is anincreasing function of N in all practical cases. Therefore, inaccordance with the present invention, the number of spreading codes Nis preferably maximized in order to maximize the total capacity of thechannel. This is different from typical HSDPA TFRC selection approachesthat do not attempt to maximize the number of spreading codes N used forcommunication with a particular WTRU.

The number of spreading codes N is limited by the total number ofavailable spreading codes M such that N≦M. In accordance with apreferred embodiment of the present invention, the number of spreadingcodes N may also be limited by the code rate used for error correctionon the physical channel. Coding techniques, such as convolutional codesand turbo codes, are used to add redundancy to transmitted informationto correct bit errors that occur in the channel and at the receiver, andthe code rate (also called coding rate) is the fraction of non-redundantdata bits in a transmitted packet. For example, if for each data bit,one redundant bit is added by the encoder, the resulting code rate is ½.According to HSDPA, all error correcting codes are derived from a rate ⅓turbo code, although the actual coding rate may be adjusted based on thechannel quality indicator (CQI) information using puncturing orrepetition techniques that involve deleting or adding bits,respectively, at the encoder output. The selection of coding rate andmodulation based on channel quality information is referred to asadaptive modulation and coding (AMC).

If, as a result of AMC, the code rate is less than ⅓, then the effectivecoding gain is reduced because bit repetition, which is known to be aweak coding scheme, is required to fill the coded transport block (TB).Therefore, in accordance with a preferred embodiment of the presentinvention, the number of spreading codes N is preferably selected to beas large as possible while maintaining a ⅓ or greater channel codingrate and without exceeding the total number of available spreading codesM. The unused spreading codes may preferably be used by other WTRUscommunicating over the same channel to make full use of the physicalresources. Alternatively, a greater number of spreading codes may beused with a corresponding code rate less than ⅓ and with a lower codinggain, however, this results in fewer spreading codes being available foruse by other WTRUs.

Referring back to the theoretical channel capacity model above, each ofthe N propagation channels may experience multipath fading andinter-code interference that is present at the output of a despreader inthe receiver. By modeling the inter-code interference as additive noise,the inter-code interference has the effect of decreasing the receivedSNR at the despreader output. The multipath experienced on each of the Npropagation channels is identical (because the propagation channels arespread over the same bandwidth), the equalizer used to receive eachpropagation channel is identical and the power transmitted on eachpropagation channel is identical. Thus, the effective noise increase asa result of inter-code interference is the same in each propagationchannel and proportional to (N−1)/N, such that the actual value of theproportionality constant depends on the effectiveness of the equalizerin restoring the orthogonality of the spreading codes.

This proportionality constant is commonly referred to as thenon-orthogonality factor (NOF), and can range from 0.0 to 1.0 but istypically much less than 1.0 in advanced receivers. The overall noisepower in the channel resulting from inter-code interference is equal toNOF S(N−1), where S is the received signal power on a propagationchannel. The resulting overall channel capacity is given by

$\begin{matrix}{C = {\frac{N}{M}{{\log_{2}( {1 + \frac{S}{{N \cdot I} + {{NOF} \cdot {S( {N - 1} )}}}} )}.}}} & {{Equation}\mspace{14mu} (1)}\end{matrix}$

where I is the total interference on the received signal.

The capacity in Equation 1 is not necessarily monotone increasingdepending on the values of S, I, and NOF. Nonetheless, for practicalscenarios Equation 1 is maximized by maximizing the number of codes Nbecause the slowly decreasing logarithmic function of N is outweighed bythe linearly increasing factor of N outside of the logarithmic function.In scenarios where the values of S, I, and NOF are such that thelogarithmic function of N dominates the outside factor of N, choosingN=1 maximizes the channel capacity. However, the latter scenario islikely only to occur under very poor channel conditions in which a WTRUmay have already handed-off to another base station.

Based on the above, and in accordance with a preferred embodiment of thepresent invention, the number spreading codes N selected as part of TFRCselection is preferably maximized, as permitted by the coding rate andthe total number of available codes M, except under very poor channelconditions in which case only one spreading code N=1 is preferably used.

Also in accordance with the present invention, the modulation typeassociated with a TFRC is preferably selected to maximize channelcapacity. In the case of 3GPP systems and in particular HSDPA, theavailable modulation types are limited to, for example, quadrature phaseshift keying (QPSK) modulation, 16 quadrature amplitude modulation(16-QAM) and possibly higher order modulation such as 64 quadratureamplitude modulation (64-QAM). In accordance with a preferred embodimentof the present invention, a threshold test on the code rate ispreferably used to select a type of modulation from among the availablemodulation types to maximize the channel throughput, as describedfurther below.

For any particular type of modulation, the code rate must beproportionally increased with the desired signal-to-noise ratio (SNR) atthe receiver to maintain a channel throughput as close as possible tothe maximum throughput. Therefore, the code rate threshold values arepreferably determined by comparing the measured throughput for a desiredSNR for each of the available modulation techniques, and a modulationscheme is selected that achieves the highest throughput for itsassociated coding rate. By way of example, consider an HSDPA downlinkchannel that supports QPSK, 16-QAM and 64-QAM modulations. FIG. 3illustrates an example of the empirically measured channel throughputfor different SNR values at the receiver for each of the availablemodulation techniques. The code rate CR_(QPSK) where the QPSK and 16-QAMthroughput curves cross, and code rate CR16-QAM where the 16-QAM and64-QAM throughput curves cross are determined and used as the code ratethreshold values. Given a TFRC, for each type of available modulation acorresponding code rate is determined according to the reported CQIinformation. If the corresponding code rate for QPSK is below theCR_(QPSK) threshold, then QPSK modulation is selected because itachieves the highest throughput for that coding rate compared to 16-QAMand 64-QAM as shown in FIG. 3. If the code rate associated with QPSKmodulation is greater than the threshold CR_(QPSK), and the code rateassociated with 16-QAM modulation is less than CR16-QAM, then 16-QAM isselected to maximize throughput. If the code rate for 16-QAM is greaterthan CR16-QAM, then 64-QAM is selected to maximize throughput. Anexample of a possible code rate threshold for QPSK is CR_(QPSK)≈0.74,which is greater than ⅓. Although choosing a modulation type for TFRCselection has been described for QPSK, 16-QAM and 64-QAM, the presentinvention may be extended to select a modulation type from among anynumber of modulation techniques, including, but not limited to,additional higher order modulations, or between QPSK and 16-QAM onlywhen 64-QAM is not available.

FIGS. 4A and 4B illustrate the steps of a preferred method 200 forgenerating and selecting TFRCs in accordance with the present inventionthat includes the various embodiments discussed above for selecting anumber of spreading codes and modulation type. The TFRC selectionpresented in FIGS. 4A and 4B is preferably performed by a TFRC selectionfunction component 108 in FIG. 2 prior to a TTI.

Referring to FIG. 4A, in step 205 the maximum number of spreading codesM available for use on the physical channel is determined based on theresource allocation scheme and the receiver capabilities of thereceiving WTRU. Recall that for HSDPA, the transmitting base station mayuse up to 15 spreading codes, and the number of spreading codessupported by the receiving WTRU is given by its UE physical layercategory. In step 210, a set of possible TFRCs are generated that matchthe channel characteristics implied by the reported CQI value and thatmeet a minimum desired TB success probability. The channelcharacteristics are preferably a maximum expected data rate for thedownlink channel, which may be known at the base station for a given CQIlevel or explicitly provided by the WTRU. Generating a possible TFRCincludes generating a transport block set size (TBSS), a number ofspreading codes and a modulation type which, when applied to atransmitted TB, have an expected data rate close to the maximum expecteddata rate of the downlink channel and meet the desired TB successprobability following decoding at the receiving WTRU. The expected datarate for a given TFRC may be determined, for example, by simulation. Asdiscussed above, the desired TB success probability for the downlinkchannel is preferably a predetermined value that is known to both thetransmitting base station and the receiving WTRU.

In step 215, the set of possible TFRCs are grouped according to commonTBSS. In each group a TFRC is preferably selected that has a largestnumber of spreading codes, up to the determined maximum number ofspreading codes M, for which the associated code rate is at least ⅓ forat least one type of available modulation scheme. Types of modulationmay include QPSK modulation, 16-QAM modulation and any other higherorder modulations. The TFRCs that are not selected are preferablydiscarded.

For every selected TFRC, beginning at step 220, a modulation type isassociated with the selected TFRC based on a code rate threshold test instep 230. Determining code rate threshold values is described above withrespect to FIG. 3. FIG. 4B gives a particular example of a code ratethreshold test for selecting a modulation type when QPSK, 16-QAM and64-QAM modulations are available. The code rate associated with QPSKmodulation is compared to a predetermined threshold in step 232. If thatcode rate is below CR_(QPSK), QPSK modulation is associated with theselected TFRC in step 233. If the code rate is above CR_(QPSK), then thecode rate associated with 16-QAM modulation is compared to thresholdCR_(16-QAM) in step 235. If that code rate is below CR_(16-QAM), then16-QAM is associated with the selected TFRC in step 236. Otherwise,64-QAM is associated with the selected TFRC in step 238. Referring toFIG. 4A, each selected TFRC is thereafter preferably saved in a list instep 240.

When the listing of the selected TFRCs is completed, the list ofselected TFRCs is preferably sorted in order of TBSS in step 245. Thelist represents all of the possible TFRCs for use when sending data tothe WTRU in accordance with the present invention. In step 250, one TFRCfrom among the list of selected TFRCs is provided to the PHY layer fordata transmission that preferably has the largest TBSS while maintainingthe desired TB success probability for the channel characteristicsdefined by the reported CQI value.

In accordance with a preferred embodiment of the present invention asdescribed with respect to FIGS. 4A and 4B, a new mapping of CQI valuesto preferred TFRCs can be created, an example of which is illustrated inTable 2 for a HSDPA downlink channel that supports a maximum number of15 spreading codes, QPSK and 16-QAM modulation and a TB successprobability of 0.9. A CQI of 0 is used when the receiving WTRU is out ofrange to receive signals on the downlink channel.

TABLE 2 CQI mapping for TFRC selection according to the presentinvention for a HSDPA downlink channel with a category 10 UE supportinga maximum of 15 spreading codes and QPSK or 16-QAM modulation Number ofspreading CQI Code rate TBSS codes Modulation 0 N/A N/A Out of range 10.14271 137 1 QPSK 2 0.18021 173 1 QPSK 3 0.21771 209 1 QPSK 4 0.26771257 1 QPSK 5 0.33021 317 1 QPSK 6 0.40521 389 1 QPSK 7 0.56771 545 1QPSK 8 0.39115 751 2 QPSK 9 0.35972 1036 3 QPSK 10 0.35313 1356 4 QPSK11 0.3191 1838 6 QPSK 12 0.35149 2362 7 QPSK 13 0.34502 2981 9 QPSK 140.32656 3762 12 QPSK 15 0.32389 4664 15 QPSK 16 0.38056 5480 15 QPSK 170.45514 6554 15 QPSK 18 0.52528 7564 15 QPSK 19 0.59542 8574 15 QPSK 200.67493 9719 15 QPSK 21 0.75146 10821 15 QPSK 22 0.43361 12488 15 16-QAM23 0.48278 13904 15 16-QAM 24 0.53753 15481 15 16-QAM 25 0.58788 1693115 16-QAM 26 0.62031 17865 15 16-QAM 27 0.66639 19192 15 16-QAM 280.70316 20251 15 16-QAM 29 0.76899 22147 15 16-QAM 30 0.88743 25558 1516-QAM

Table 2 includes the preferred TBSS, number of spreading codes andmodulation type as derived according to the present invention describedabove, and the associated coding rate, for each possible CQI value for acategory 10 WTRU. When Table 2 is compared to the CQI mapping table fora category 10 UE in 3GPP TS 125.214 as reproduced in Table 1, it isobserved that TFRC selection according to the present inventiongenerally selects a greater number of spreading codes and a larger TBSS,whenever possible and in particular for intermediate CQI values, inorder to improve overall channel throughput.

FIG. 5 shows the measured throughput on a downlink CDMA channel usingthe existing 3GPP CQI mapping as given in Table 1 compared to themeasured throughput for the optimized CQI mapping generated according tothe present invention in Table 2 for a category 10 UE for a range ofaverage SNR values and for a TB success probability of 0.9. Thethroughput is given versus an average SNR because of variations in theinstantaneous SNR as a result of fading in the channel. FIG. 5illustrates the improvement in throughput achieved by the presentinvention over existing TFRC selection techniques.

Although the features and elements of the present invention aredescribed in the preferred embodiments in particular combinations, eachfeature or element can be used alone without the other features andelements of the preferred embodiments or in various combinations with orwithout other features and elements of the present invention. Themethods or flow charts provided in the present invention may beimplemented in a computer program, software, or firmware tangiblyembodied in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

The components for implementing the invention referenced above may beimplemented as separate physical devices or combined such as in aprocessor that implements the functions of multiple components. Suitableprocessors include, by way of example, a general purpose processor, aspecial purpose processor, a conventional processor, a digital signalprocessor (DSP), a plurality of microprocessors, one or moremicroprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any integrated circuit,and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for in use in a wireless transmit receiveunit (WTRU), user equipment, terminal, base station, radio networkcontroller, or any host computer. The WTRU may be used in conjunctionwith modules, implemented in hardware and/or software, such as a camera,a video camera module, a videophone, a speakerphone, a vibration device,a speaker, a microphone, a television transceiver, a hands free headset,a keyboard, a Bluetooth® module, a frequency modulated (FM) radio unit,a liquid crystal display (LCD) display unit, an organic light-emittingdiode (OLED) display unit, a digital music player, a media player, avideo game player module, an Internet browser, and/or any wireless localarea network (WLAN) module.

1. A method for generating and selecting transport format resourcecombinations (TFRCs) in a medium access control layer of a wirelesstransmit receive unit (WTRU) to be used for transmission of data over acode division multiple access (CDMA) channel in a wireless communicationsystem, wherein a TFRC includes a transport block set size (TBSS) value,a number of spreading codes, and a type of modulation, the methodcomprising: determining a maximum number of spreading codes fortransmission; generating a set of possible TFRCs and grouping thepossible TFRCs according to common TBSS value; from each group ofpossible TFRCs, selecting a TFRC that has the largest number ofspreading codes not greater than the determined maximum number ofspreading codes and that has a corresponding code rate at least equal toa minimum code rate; selecting a type of modulation for each selectedTFRC by comparing at least one corresponding code rate to at least onepredetermined threshold; and providing one of the selected TFRCs to aphysical (PHY) layer to be used for data transmission over the CDMAchannel.
 2. The method of claim 1 wherein the determining a maximumnumber of spreading codes is based on a resource allocation schemeassociated with the CDMA channel.
 3. The method of claim 1 furthercomprising receiving from the PHY layer a channel quality indicator(CQI) value corresponding to the CDMA channel, wherein: the generating aset of possible TFRCs and the providing one of the selected TFRCs to thePHY layer is based at least in part on the received CQI value and apredetermined transport block (TB) success probability associated withthe CDMA channel.
 4. The method of claim 3 wherein a predetermined TBsuccess probability of approximately 0.9 is utilized.
 5. The method ofclaim 3 wherein the CQI value that is received is an integer value from1 to 30 having a known corresponding mapping to a TBSS value, a numberof spreading codes and a modulation type that correspond tocharacteristics of the CDMA channel.
 6. The method of claim 3 whereinthe CQI value that is received is an integer value from 1 to 30 having aknown corresponding mapping to a TBSS value, a number of spreading codesand a modulation type that corresponds to at least a maximum expecteddata rate characteristic of the CDMA channel.
 7. The method of claim 6wherein the generating a set of possible TFRCs and providing one of theselected TFRCs to the PHY layer is based on matching a data ratecorresponding to a TFRC to the maximum expected data rate characteristicof the CDMA channel and the predetermined TB success probability.
 8. Themethod of claim 7 wherein the providing one of the selected TFRCs to thePHY layer is further based on choosing one of the selected TFRCs with alargest corresponding TBSS value.
 9. The method of claim 3 performed ina base station wherein the CDMA channel is a downlink channel.
 10. Themethod of claim 9 further comprising: receiving the CQI value in thebase station PHY layer via an uplink channel that has been determined bymeasuring a maximum expected data rate of the downlink channel.
 11. Themethod of claim 10, wherein the CQI value is determined as proportionalto the measured maximum expected data rate, and wherein selecting a TFRCfrom each group of possible TFRCs is according to the TFRC that hasexactly 1 spreading code for low CQI values for which 1 spreading codemaximizes a theoretical CDMA channel capacity.
 12. The method of claim11 wherein the low CQI values include CQI values no greater than
 7. 13.The method of claim 1 further comprising maintaining the selected TFRCsin a list and sorting the list according to TBSS value.
 14. The methodof claim 1 wherein a turbo code rate equal to ⅓ is used as the minimumcode rate.
 15. The method of claim 1 wherein the type of modulation partof a TFRC is one of quadrature phase shift keying (QPSK) modulation and16 quadrature amplitude modulation (16-QAM).
 16. The method of claim 15wherein the selecting a type of modulation for each selected TFRCincludes determining the at least one corresponding code rate for eachselected TFRC when the type of modulation is assumed to be QPSK, whereinif the at least one corresponding code rate is below the at least onepredetermined threshold QPSK modulation is selected and otherwise 16-QAMis selected.
 17. The method of claim 16 wherein the type of modulationpart of a TFRC may also be 64 quadrature amplitude modulation (64-QAM),further comprising: determining a second corresponding code rate foreach selected TFRC when the type of modulation is assumed to be 16-QAM;and comparing the second corresponding code rate for each selected TFRCto a second predetermined threshold, wherein if the at least onecorresponding code rate is above the at least one predetermine thresholdand the second corresponding code rate is below the second predeterminedthreshold 16-QAM is selected, and if the second corresponding code rateis above the second predetermined threshold 64-QAM is selected.
 18. Themethod of claim 17 wherein the at least one predetermined threshold andthe second predetermined threshold are each in between 0 and
 1. 19. Themethod of claim 18 wherein the at least one predetermined threshold is0.74.
 20. The method of claim 17 further comprising: determining thepre-determined thresholds by measuring empirically and comparingthroughput versus received signal-to-noise ratio (SNR) for eachmodulation type.
 21. The method of claim 1 performed in a WTRUconfigured for use in a Third Generation Partnership Project (3GPP)compliant wireless communication system.
 22. The method of claim 21performed in a WTRU configured for use in a Third Generation PartnershipProject (3GPP) compliant wireless communication system with high speeddownlink packet access (HSDPA).
 23. The method of claim 22 wherein themaximum number of codes is no more than
 15. 24. The method of claim 23wherein the maximum number of codes is also according to receivercapabilities of a receiving WTRU of the CDMA channel.
 25. The method ofclaim 24 wherein the receiver capabilities are according to a physicallayer category associated with the receiving WTRU.
 26. The method ofclaim 21 performed in a WTRU configured for use in a Third GenerationPartnership Project (3GPP) compliant wireless communication system withhigh speed packet access evolution (HSPA+).
 27. A wireless transmitreceive unit (WTRU) configured with a hierarchy of processing layersincluding physical (PHY) layer, medium access control (MAC) layer andhigher layers, the WTRU comprising: a MAC layer transport formatresource combination (TFRC) selection function component configured togenerate and select transport format resource combinations (TFRCs) to beused for transmission of data over a CDMA channel, wherein a TFRCincludes a transport block set size (TBSS) value, a number of spreadingcodes, and a type of modulation, the TFRC selection function componentfurther configured to: determine a maximum number of codes available fortransmission; generate a set of possible TFRCs and group the possibleTFRCs according to common TBSS value; select a TFRC from each group ofpossible TFRCs that has the largest number of spreading codes notgreater than the determined maximum number of codes and that has acorresponding code rate at least equal to a minimum code rate; select atype of modulation for each selected TFRC by comparing at least onecorresponding code rate to at least one predetermined threshold; andprovide one of the selected TFRCs to the PHY layer to be used for datatransmission over the CDMA channel.
 28. The WTRU of claim 27 wherein theTFRC selection function component is configured to determine a maximumnumber of spreading codes based on a resource allocation schemeassociated with the CDMA channel.
 29. The WTRU of claim 27 wherein theTFRC selection function component is further configured to receive fromthe PHY layer a channel quality indicator (CQI) value corresponding tothe CDMA channel, wherein: the TFRC selection function component isconfigured to generate a set of possible TFRCs, and provide one of theselected TFRCs to the PHY layer according to the CQI value and apredetermined transport block (TB) success probability associated withthe CDMA channel.
 30. The WTRU of claim 29 wherein the TFRC selectionfunction component is configured to use a TB success probability ofapproximately 0.9 as the predetermined TB success probability.
 31. TheWTRU of claim 29 wherein the TFRC selection function component isconfigured to receive as a CQI value an integer value from 1 to 30 witha known corresponding mapping to a TBSS value, a number of spreadingcodes and a modulation type that correspond to characteristics of theCDMA channel.
 32. The WTRU of claim 29 wherein the TFRC selectionfunction component is configured to receive as a CQI value an integervalue from 1 to 30 with a known corresponding mapping to a TBSS value, anumber of spreading codes and a modulation type that correspond to amaximum expected data rate characteristic of the CDMA channel.
 33. TheWTRU of claim 32 wherein the TFRC selection function component isconfigured to generate a set of possible TFRCs and provide one of theselected TFRCs to the PHY layer by matching a data rate corresponding toa TFRC to the maximum expected data rate characteristic of the CDMAchannel and the predetermined TB success probability.
 34. The WTRU ofclaim 33 wherein the TFRC selection function component is configured toprovide one of the selected TFRCs to the PHY layer based on choosing oneof the selected TFRCs with a largest corresponding TBSS value.
 35. TheWTRU of claim 27 configured as a base station wherein the CDMA channelis a downlink channel.
 36. The base station of claim 35 configured toreceive the CQI value by the base station PHY layer via an uplinkchannel that is determined by measuring a maximum expected data rate ofthe downlink channel transmitted by the base station.
 37. The WTRU ofclaim 36 wherein the CQI value is proportional to the measured maximumexpected data rate, and wherein the TFRC selection function component isconfigured to select a TFRC from each group of possible TFRCs accordingto the TFRC that has exactly 1 spreading code for low CQI values forwhich 1 spreading code maximizes a theoretical CDMA channel capacity.38. The WTRU of claim 37 wherein the TFRC selection function componentis configured to use as the low CQI values a value no greater than 7.39. The WTRU of claim 27 wherein the TFRC selection function componentis further configured to maintain the selected TFRCs in a list and sortthe list according to TBSS.
 40. The WTRU of claim 27 wherein the TFRCselection function component is configured to use as the code rate aturbo code rate that has a minimum code rate equal to ⅓.
 41. The WTRU ofclaim 27 configured to use as the type of modulation part of a TFRC, oneof quadrature phase shift keying (QPSK) modulation and 16 quadratureamplitude modulation (16-QAM).
 42. The WTRU of claim 41 wherein the TFRCselection function component is configured select a type of modulationfor each selected TFRC by determining the at least one correspondingcode rate for each selected TFRC when the type of modulation is assumedto be QPSK, wherein if the at least one corresponding code rate is belowthe at least one predetermined threshold QPSK modulation is selected andotherwise 16-QAM is selected.
 43. The WTRU of claim 42 wherein the typeof modulation part of a TFRC may also be 64 quadrature amplitudemodulation (64-QAM), wherein the TFRC selection function component isfurther configured to: determine a second corresponding code rate foreach selected TFRC when the type of modulation is assumed to be 16-QAM;and compare the second corresponding code rate for each selected TFRC toa second predetermined threshold, wherein if the at least onecorresponding code rate is above the at least one predetermine thresholdand the second corresponding code rate is below the second predeterminedthreshold 16-QAM is selected, and if the second corresponding code rateis above the second predetermined threshold 64-QAM is selected.
 44. TheWTRU of claim 27 wherein the TFRC selection function component isconfigured to use as the at least one predetermined threshold and as thesecond predetermined threshold values that are between 0 and
 1. 45. TheWTRU of claim 27 wherein the TFRC selection function component isconfigured to use as the at least one predetermined threshold a value of0.74.
 46. The WTRU of claim 27 configured to operate in a ThirdGeneration Partnership Project (3GPP) compliant wireless communicationsystem.
 47. The WTRU of claim 27 configured to conduct wirelesscommunication according to high speed downlink packet access (HSDPA).48. The WTRU of claim 47 configured to use no more than 15 codes as themaximum number of codes.
 49. The WTRU of claim 48 configured todetermine the maximum number of codes according to capabilities of aWTRU that receives the CDMA channel.
 50. The WTRU of claim 27 configuredto conduct wireless communication according to high speed downlinkpacket access evolution (HSDPA+).